Generally, the valve assembly for the injection molding machine is for injecting a liquid resin into a cavity of a metallic mold, wherein the liquid resin is supplied from a cylinder (also referred to as an extruder) in which a resin is molten. The valve assembly is designed to open or close a gate by a upward or downward movement of a valve pin, and is generally classified into two types: manifold and cylinder, according to the number of parts (or molds) molded at a time wherein the manifold type is used to mold multiple molds from the liquid resin supplied through a manifold, while the cylinder type is used to mold a single mold from the liquid resin supplied through a cylinder.
FIG. 1 is a cross-sectional view showing a valve gate assembly for a conventional injection molding machine (U.S. Pat. No. 6,343,925/HOT RUNNER VALVE GATE PISTON ASSEMBLY). As shown, the valve gate assembly is generally comprised of a driver 100 and a valve body 200. As a driving power source for an upward or downward movement of a valve pin 210, high-pressure air is used.
Specifically, the driver 100 is provided with a plurality of air passageways or channels 110 and 120 for supplying and discharging the high-pressure air from/toward an outside. An air piston 140 in an cylinder 130 ascends or descends through the plurality of channels 110 and 120. A valve pin 210 is cooperatively coupled to a lower end of the piston 130. Thus, the valve pin 210 is raised or lowered with the piston 130, and thereby a gate 220 of the valve body 200 is selectively closed or opened.
Meanwhile, the valve body 200 is provided with a resin channel 230 which is spaced around the valve pin 210. The resin channel 230 is connected with the gate 220 on one end and with a resin channel 310 of a manifold 300 on the other end.
In the valve gate assembly for the injection molding machine constructed in this manner, when the high-pressure operation air is selectively supplied to the air channels 110 and 120, the piston 140 is raised or lowered. Simultaneously, the valve pin 210 is also raised or lowered. Therefore, raising or lowering of the piston 140 causes the gate 220 to be opened or closed. Eventually, the resin, which has been supplied through the manifold 300, is either supplied through the gate 220 to a metallic mold or blocked.
To sum up, the valve gate assembly for the conventional injection molding machine operated by the air pressure supplies the high-pressure air through the selected air channel 110 or 120 to the cylinder 130, thereby raising or lowering the piston 140. In cooperation with the piston 140, the valve pin 210 opens or closes the gate 220.
However, the conventional valve gate assembly constructed as above makes use of the air as the operation source for raising or lowering the valve pin 210. As a result, there is a problem in that it has a slow responsibility and a low reliability on operation. Particularly, an airtight structure must be employed in order to prevent the high-pressure air, the operation source, from leaking out. This incurs another problem in that the assembly has an increased entire volume and a complicated structure, so that it is considerably restricted in installation space. Consequently, a degree of freedom in design of metallic molds is limited as well as maintenance and management are not easy.
In order to these problems, a valve assembly is proposed as shown in FIG. 2, which is electrically powered to generate a driving force, and thus actuating a valve pin.
Looking at a configuration of an electrically powered valve assembly as shown in FIG. 2, it is generally comprised of a valve body 500 and a driving means 600. The valve body 500 has a structure of a typical valve body, which is provided with a resin channel 510 for injecting a resin into a metallic mold through a gate formed at a leading end of the valve body, wherein the resin is supplied from a resin channel 710 formed in a manifold 700.
The driving means 600 is designed to include an actuator for raising and lowering a valve pin 530 through supply of power. The actuator is configured in such a manner that first and second tubular electromagnets 610 and 620 are vertically disposed at a distance apart from each other and selectively generate a magnetic force, and a core 630 magnetized by the magnetic force is installed between the electromagnets 610 and 620. Here, the core 630 is supported by an elastic spring 640 for restoring the valve pin on its upper surface.
The valve assembly of the electrically powered valve assembly constructed in this manner can be made in a small size by employing the actuator as the driving source, so that it is possible not only to increase a degree of freedom in design of metallic molds, but also to rapidly and precisely control a movement amount of the valve pin.
However, because the valve assembly of the electrically powered valve assembly employs the actuator as the driving source, it has disadvantages in that an opening/closing amount of the gate can not be controlled, and that an ambient temperature is high during injection molding, components, such as a coil and circuitry, constituting the actuator is deteriorated, and thus there is a need for frequent repairs, which results in a lowered reliability. Particularly, in the case that the valve assembly is applied to a metallic mold capable of molding a plurality of molds at a time, it is not easy to perform exchange or repair of the driving source, so that workability and productivity are decreased.